1. Field of the Invention
The present invention relates to an assembling structure and an assembling method of an indicating needle to an indicating needle shaft in a stepping motor incorporated instrument.
2. Description of Prior Art
Generally, an instrument such as a speed meter for a vehicle, and the like is provided with a case body 3 comprising an upper case 1 and a lower case 2, and an indicating needle 5 is rotatably pivoted at an upper portion to the upper case 1, and at a lower portion to the lower case 2, respectively, and also has a gear 4 at an intermediate portion. A top portion 5A of the indicating needle shaft 5 is projected outside from the upper case 1, and is provided with an indicating needle 6.
A press fit method is generally used for assembling the indicating needle 6 to the top portion 5A of the indicating needle shaft 5. That is, generally, the case body 3 is flatly placed on a base (not shown), directing the indicating needle shaft 5A in a direction perpendicular to the case body 3, and with this state, a hole 6A for the indicating needle 6 is aligned with the top portion 5A of the indicating needle shaft 5, then the indicating needle 6 is pressed into the top portion 5A of the indicating needle shaft 5 by pressing the indicating needle 6 downwardly as shown by the allow in FIG. 7.
However, a conventional instrument for a vehicle comprises a concave shaft bearing 2A inside the lower case 2, and has a structure that a lower end portion 5B for the indicating needle shaft 6 is pivoted by this shaft bearing 2A, so that the lower case 2 locally receives considerable strength from the indicating needle shaft 5 when the indicating needle 6 is pressed into the shaft. The case body including the lower case 2 is made of synthetic resin, and if the case body 3 locally receives considerable strength, it is deformed and causes problems for the strength.
As shown in FIG. 8, there is a method for spreading the strength that applies to the lower case 2 when the indicating needle 6 is pressed, by bringing a boss 4A of the gear 4, which is in the intermediate portion of the indicating needle shaft 5 into contact with a projection 2B inside the lower case 2. However, the method is not enough for protecting the lower case 2 from the deformation, and also the gear may be deformed.
Accordingly, there has been proposed a method that a through-hole is formed on a lower case, a jig is mounted to the lower side of the lower case while the lower end portion of the indicating needle shaft is inserted into the through-hole, then with the state that the leading end of the lower end portion of the indicating needle is positioned on the jig, an indicating needle is pressed into the leading end of the top portion of the indicating needle shaft, so that the strength, when the indicating needle is pressed, does not directly apply to the lower case. (For example, Japanese Patent Laid-Open 2001-317970)
However, the above described prior art the through-hole is provided on the plane bottom surface of the lower case, and the opening edge portion of the through-hole and the bottom surface of the lower case have the same height. Therefore, there is a problem if the lower end portion of the indicating needle is inserted into the through-hole, the leading edge of the lower end portion of the indicating needle shaft is projected from the bottom surface of the lower case. If the leading end of the lower end portion of the indicating needle is projected from the bottom surface of the lower case, it takes time for packaging, and a package case becomes bigger. Moreover, there may be a case that the indicating needle may be deformed by shock from the outside.
When the through-hole of the lower case is processed, flashes are generated on the rim of the through-hole. Moreover, for the prior art, the opening edge portion of the through-hole and the bottom surface of the lower case have the same height, so that the rim of the through-hole is easy to be hit by another component, and if the rim of the through-hole is hit by another component, flushes are entered inside the through-hole, and it becomes a problem for stabilizing the rotation of the indicating needle shaft.